1. Field of the Invention
The present invention relates generally to an apparatus and method for allocating resources in a wireless communication system, and more particularly, to an apparatus and method for allocating frequency resources in an Orthogonal Frequency Division Multiple Access (OFDMA) wireless communication system.
2. Description of the Related Art
Recently, in wireless communication systems, intensive research has been conducted on Orthogonal Frequency Division Multiplexing (OFDM) and/or OFDMA as a scheme suitable for high-speed data transmission in wireless channels. OFDM, a scheme for transmitting data using multiple carriers, is a kind of Multi-Carrier Modulation (MCM) that converts a serial input symbol stream into parallel symbol streams, and modulates each of them with multiple orthogonal subcarriers, i.e., multiple orthogonal subcarrier channels before transmission.
FIG. 1 is a diagram illustrating a transmitter structure of a general OFDM system.
An OFDM transmitter includes a channel encoder 101, a modulator 102, a Serial-to-Parallel (S/P) converter 103, an Inverse Fast Fourier Transform (IFFT) unit 104, a Parallel-to-Serial (P/S) converter 105 and a Cyclic Prefix (CP) inserter 106. The channel encoder 101, also known as a channel-encoding block, performs channel coding on an input information bit stream. Generally, a convolutional encoder, turbo encoder, a Low Density Parity Check (LDPC) encoder, etc. are used as the channel encoder 101. The modulator 102 generates modulation symbols by performing modulation, such as Quadrature Phase Shift Keying (QPSK), 8-ary Phase Shift Keying (8PSK), 16-ary Quadrature Amplitude Modulation (16-QAM), 64-QAM, 256-QAM, etc., on the output of the channel encoder 101. Although not illustrated in FIG. 1, a rate-matching block for performing repetition and puncturing can be further interposed between the channel encoder 101 and the modulator 102. The S/P converter 103 serves to convert the output of the modulator 102 into parallel data.
The IFFT unit 104 performs IFFT calculation on the output of the S/P converter 103. The output of the IFFT unit 104 is converted into serial data by the P/S converter 105. A CP inserter 106 inserts a CP code into the output of the P/S converter 105. The Long Term Evolution (LTE) system now under discussion as the next generation wireless communication system of the Universal Mobile Telecommunication Service (UMTS) system in the 3rd Generation Partnership Project (3GPP) standard group for asynchronous communication, uses Single Carrier Frequency Division Multiple Access (SC-FDMA) for the uplink to solve the increase in Peak-to-Average Power Ratio (PAPR), which is a defect of the OFDMA scheme. SC-FDMA, a kind of the OFDM scheme, can be realized by adding a Fast Fourier Transform (FFT) unit in front of the IFFT unit 104, and precoding the data before it undergoes IFFT calculation in the IFFT unit 104.
FIG. 2 schematically illustrates resources of a general OFDM system.
As shown in FIG. 2, in OFDM or SC-FDMA, wireless resources are expressed in a two-dimensional arrangement in time and frequency domains. In FIG. 2, the horizontal axis represents a time domain 201, and the vertical axis represents a frequency domain 202. In the time domain 201, 7 OFDM symbols constitute one 204, and two slots constitute one subframe 205. Generally, one subframe 205 has the same length as a Transmission Time Interval (TTI), which is a basic transmission unit.
FIG. 3 is a diagram illustrating a data transmission/reception procedure between a base station and a terminal in a general OFDM system.
In step 303, a terminal (or User Equipment (UE)) 320 generates a Channel Quality Indicator (CQI) indicating the downlink channel condition by measuring a Reference Signal (RS) such as a pilot, transmitted by a base station (or Node B) 310. In step 304, the terminal 320 transmits the CQI to the base station 310. In this case, the terminal 320 can transmit a Channel Sounding Reference Signal (CS/RS) along with the CQI so that the base station 310 can detect the uplink channel condition. Upon receipt of the CQI and/or CS/RS, the base station 310 performs scheduling in step 305, to determine downlink or uplink resources it will allocate to the terminal 320. In step 306, the base station 310 transmits a scheduling grant indicating the determined downlink/uplink resources to the terminal 320. Then the terminal 320 checks in step 307 whether the scheduling grant is delivered to the terminal 320 itself. If it is checked in step 307 that the scheduling grant is transmitted to the terminal 320 itself, the terminal 320 detects, in step 308, downlink/uplink resources indicated by the scheduling grant and performs data exchange with the base station 310 using the allocated downlink/uplink resources.
In the scheduling process, the base station 310 delivers the information necessary for data transmission/reception to the terminal 320 using a scheduling grant, and the scheduling grant is transmitted to the terminal 320 over a forward Physical Downlink Control Channel (PDCCH). The PDCCH uses some of the resources shown in FIG. 2. The base station 310 selects one or multiple PDCCHs from among available PDCCHs, and transmits the scheduling grant to the terminal 320 through the selected PDCCH(s).
The scheduling grant includes therein several types of information, and its typical information can include the amount of packet information, a modulation method, allocated resources, and Hybrid Automatic Repeat reQuest (HARQ) information. Of the above-stated information, the information on the allocated resources can have an important meaning in the OFDMA communication system. In the OFDMA communication system, a frequency band can be divided into a part having a good channel response and a part having a bad channel response at an arbitrary time. Allocating resources in the good channel response frequency band to the terminal is required to increase the performance of frequency-selective scheduling. Therefore, there is a need for a resource allocation method capable of maximally increasing the performance of the frequency-selective scheduling.
FIG. 4 is a diagram illustrating a frequency resource allocation method in a general OFDM system.
The frequency resource allocation method of FIG. 4 illustrates a start point of a resource block set and the number of resource blocks. In FIG. 4, an entire frequency bandwidth 401 is composed of N Resource Blocks (RBs), and when there is a wish to allocate a resource block #6 402 through a resource block #9 403 to an arbitrary terminal, the resource allocation information included in a scheduling grant includes a start point 404 (i.e., resource block #6 402) of the allocated resources and a number of the allocated resource blocks 405.
FIG. 5 is a diagram illustrating frequency resources allocated in a general OFDM system.
FIG. 5 shows several cases for a set of frequency resource blocks allocated to an arbitrary terminal. Reference numeral 501 represents a case where one consecutive resource block set is allocated to one terminal. Reference numeral 502 represents a case where multiple consecutive resource block sets are allocated to one terminal. Reference numeral 503 represents a case where the entire resource block is allocated to one terminal. In the cases 501 and 503, the resource allocation method of FIG. 4 can perform resource allocation with one start point and the number of resource blocks. However, in the case 502 where there is an intention to allocate resource block sets 511, 512 and 513 to one terminal, since multiple consecutive resource block sets are available for resource allocation, it is necessary to indicate the start point and the number of resource blocks separately for each of the consecutive resource block sets.
In order to increase frequency-selective scheduling performance of the OFDMA communication system, consideration should be given to the case 502 where multiple consecutive resource block sets are available. However, in providing information on the start point of the resource block sets and the number of resource blocks for resource allocation, as the amount of information that should be signaled varies according to the number of consecutive resource block sets, there are several formats for scheduling grant channels transmitted to the terminal. When there are several formats for scheduling grant channels, since the terminal cannot judge whether a corresponding scheduling grant channel is a channel transmitted to the terminal itself unless it decodes all the channels in the several formats, its reception complexity increases with the number of formats of the scheduling grant channels. In addition, the base station should transmit many scheduling grant channels, causing a reduction in efficient utilization of resources.